The Cysteamine Study provided answers to the question of the drug's efficacy with some inferential difficulty, since cysteamine's unpleasant taste and smell rendered it unpalatable to many patients, who subsequently did not receive effective amounts of the drug. The design of the study itself, with no randomized concurrent control group, obscured effects and required a good deal of reliance on adjustment techniques in the final analysis. The object of the current study is to improve treatment of cystinosis and determine more of the effects of cysteamine. In the drug development phase of the trial, investigation of a cysteamine analog, phosphocysteamine, revealed that it converts rapidly to cysteamine in the bloodstream, so that the two drugs are effective equivalents. Moreover, since the taste and smell of phosphocysteamine are less obnoxious to some patients, it serves as an alternative treatment that may improve patient compliance. The current study randomizes patients to a low dose of cysteamine (or phosphocysteamine as the patient chooses) or to a high dose; so designed the trial is an optimal vehicle for ascertaining the best course of treatment. Patient recruitment and treatment is coordinated at contracted study center at the University of California, San Diego. Data center functions are the responsibility of the University of Texas Health Science Center at Dallas. The study will encompass 3-4 years of enrollment and treatment of at least 90 patients. The treatments will be evaluated on the basis of renal function as measured by serum creatinine levels and creatinine clearance, as a surrogate of glomerular filtration rate, at the end of the study.